Remarkably Improved Durability of Ni-Co Dispersed Samaria-Doped Ceria Hydrogen Electrodes by Reversible Cycling Operation of Solid Oxide Cells

We have examined the durability of a double-layer hydrogen electrode, consisting of a samaria-doped ceria (SDC) scaffold with highly dispersed Ni-Co nanoparticles as the catalyst layer and a thin current collecting layer of Ni-yttria-stabilized zirconia (YSZ) cermet for a reversible solid oxide cell (R-SOC). When steam electrolysis was performed continuously (solid oxide electrolysis cell, SOEC) at 800 °C, a rapid, large increase in the ohmic resistance of the hydrogen electrode side was observed. In contrast, the durability of the hydrogen electrode was found to be improved remarkably by reversible cycling operation between SOEC and solid oxide fuel cell (SOFC) modes, i.e., virtually no degradation over 1200 h. This could be ascribed to a stabilization of the microstructure of the hydrogen electrode. It was also found that the durability of the oxygen electrode, which was based on a composite of La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) and SDC with an SDC interlayer, was also improved by the reversible cycling operation, compared with a slight degradation in the continuous SOEC operation.